This Application is entitled to the benefit of and incorporates by reference essential subject matter disclosed in Japanese Patent Applications No. 2001-315289 filed Oct. 12, 2001 and No.2001-350138 filed Nov. 15, 2001.
1. Field of the Invention
The present invention relates to a compression-ignition internal combustion engine, and more particularly to a compression-ignition internal combustion engine designed to clean exhaust gas by improving combustion features.
2. Description of the Related Art
Demand for environmental compliance concerning internal combustion engines, and more particularly diesel engines, has recently increased, and there is an urgent need to improve exhaust gas. Consequently, although various post-treatment techniques such as diesel particulate filters (DPF) for collecting black smoke and other types of soot, and NOx catalysts for reducing and cleaning NOx are making remarkable progress, methods for improving combustion features as such must still involve drastic measures.
Common diesel combustion is performed using diffusion combustion, which is a combustion mode in which single-stage (one-time) fuel injection is performed near the top dead center of compression (usually about 10xc2x0 BTDC to 10xc2x0 ATDC) at which cylinder pressure and temperature has sufficiently increased; the fuel is partially ignited after a specific ignition delay time expires; the fuel is evaporated, mixed with air, and combusted according to diffusion of the fuel; and combustion is conducted while the flames are turbulently diffused in sequence.
However, various improvements have been made concerning the recent increase in demands for reducing smoke and NOx in exhaust gas. Exhaust gas recirculation (EGR) has been known in the past to be effective for reducing NOx, and is now in wide use. However, since EGR entails refluxing the exhaust gas, worsening of the smoke problem cannot be avoided.
In certain cases of regular combustion, cylinder pressure may suddenly increase as a result of rapid initial combustion, and loud combustion noise may occur. In order to prevent this, a two-stage injection process is conducted wherein a pilot injection of a small amount is executed prior to the main injection (primary injection), which is done at regular timing. In this case, after the fuel is ignited by the pilot injection and an ignition source is created, the fuel from the main injection is burned using the ignition source, whereby rapid initial combustion and a rapid increase in cylinder pressure are suppressed, and combustion noise is prevented. The combustion features at this point are substantially identical to diffusion combustion.
However, such regular pilot/main injection is disadvantageous in that the smoke problem is exacerbated when pilot injection is conducted.
Recently, new combustion systems have been proposed in regards to these techniques. One is known as modulated kinetics (MK) combustion, aimed at simultaneously reducing NOx and smoke. This can also be referred to as low-temperature premixed combustion, and the summary thereof is as follows. Specifically, since lowering combustion temperature is effective in reducing NOx, this is done by comparatively massive EGR. There is the concern that smoke will increase if this approach is adopted, but this is dealt with by premixing the fuel. Premixing involves two methods, which are advanced injection wherein fuel is injected earlier than normal, and retarded injection wherein fuel is injected later than normal, but retarded injection is employed because of difficulty with ignition time control in advanced injection. In summary, MK combustion involves the simultaneous reduction of NOx and smoke by combining massive EGR and retarded injection. Reference literature includes xe2x80x9cProceedings of the Automobile Engineering Society,xe2x80x9d vol. 28, No. 1, 1997-1, p. 41; and Ibid., vol. 28, No. 2, 1997-4, p. 29.
With MK combustion, however, single-stage injection is conducted beyond the top dead center of compression, and ignition and combustion are slowly done after a comparatively long premixing time, so fuel consumption tends to deteriorate, combustion becomes unstable due to low cylinder pressure, and accidental flameouts or white smoke are apt to occur. Since this procedure is based on massive EGR, it is impossible to expect that a significant smoke reduction effect can be obtained.
As shown in Japanese Patent Application Laid-open No. 2000-310150, pilot injection is conducted earlier than normal, and there are devices in which main injection is performed with timing that may cause accidental flameouts without primary injection. This is intended to further reduce NOx.
Although this is effective in reducing NOx, it also results in worsening of smoke because continuous combustion induced by the pilot injection occurs prior to the main injection and smoke is produced as a result of combustion induced by the pilot injection.
Consequently, it is difficult to improve smoke with these techniques, which may not necessarily be sufficient to satisfy strict regulations in the future
The present invention was therefore devised in view of the above, and an object thereof is to suppress smoke by optimizing the quantity and timing of the pilot injection in a compression-ignition internal combustion engine in which pilot injection is performed and main injection is carried out beyond the top dead center of compression.
Another object of the present invention is to control the instability of combustion in the low-load areas of an engine.
The present invention is a compression-ignition internal combustion engine comprising a fuel injection valve for injecting fuel into a combustion chamber in a cylinder, the fuel injection quantity and the fuel injection timing being controlled based on the engine operating conditions; wherein pilot injection of a comparatively small quantity is carried out through the fuel injection valve prior to the top dead center of compression, and main injection of a comparatively large quantity is then carried out through the fuel injection valve beyond the top dead center of compression; and the fuel injection quantity and fuel injection timing for the pilot injection are set such that the maximum rate of heat release induced by the pilot injection is 60 kJ/s or less.
The timing on the most spark-advanced side of the pilot injection should preferably correspond to the time of a crank angle at which the fuel injected through the fuel injection valve moves past the inlet edge of the cavity formed at the top of the piston.
The EGR performed by an EGR apparatus should preferably be carried out according to the pilot injection and main injection.
The above-mentioned compression-ignition internal combustion engine may be a common-rail diesel engine.
The present invention is a common-rail diesel engine comprising a fuel injection valve for injecting fuel into a combustion chamber in a cylinder, a common rail for constantly supplying high-pressure fuel to the fuel injection valve, and control means for controlling the fuel injection valve such that the quantity and timing of the fuel injected through the fuel injection valve are equivalent to the quantity and timing determined in advance based on the operating conditions of the engine; wherein the control means carries out pilot injection of a comparatively small quantity through the fuel injection valve prior to the top dead center of compression and then carries out main injection of a comparatively large quantity through the fuel injection valve beyond the top dead center of compression, and the pilot injection is carried out based on the fuel injection quantity and fuel injection timing such that the maximum rate of heat release induced by the pilot injection is 60 kJ/s or less.
The present invention is a method for controlling a compression-ignition internal combustion engine configured such that the quantity and timing of the fuel injected through the fuel injection valve into the combustion chamber in the cylinder is controlled based on the operating conditions of the engine; wherein pilot injection of a comparatively small quantity is carried out through the fuel injection valve prior to the top dead center of compression, and main injection of a comparatively large quantity is then carried out through the fuel injection valve beyond the top dead center of compression; and the fuel injection quantity and fuel injection timing in the pilot injection are set such that the maximum rate of heat release induced by the pilot injection is 60 kJ/s or less.
The present invention is a compression-ignition internal combustion engine comprising a fuel injection valve for injecting fuel into a combustion chamber in a cylinder, the quantity and timing of the fuel injected through the fuel injection valve being controlled based on the engine operating conditions; wherein the apparatus comprises as fuel injection control modes a first injection mode in which pilot injection is carried out through the fuel injection valve with a fuel injection quantity and fuel injection timing such that the maximum rate of heat release induced by the pilot injection is 60 kJ/s or less, and main injection is then carried out through the fuel injection valve at a timing beyond the top dead center of compression; and a second injection mode in which pilot injection and main injection are carried out through the fuel injection valve on the basis of conditions that do not fulfill the conditions of the first injection mode; and the fuel injection control modes are switched such that fuel injection control is implemented in the second injection mode in the low-load areas of the engine operating conditions, and fuel injection control is implemented in the first injection mode in the high-load areas of the engine operating conditions.
In this arrangement, regular pilot/main injection is performed instead of low-heat-rate pilot/main injection in a low-load area. Combustion instability in a low-load area can thereby be controlled.
In a low-load area of an engine, the fuel injection control modes are preferably switched such that fuel injection control is implemented in the second injection mode in a low-speed area of the engine and fuel injection control is implemented in the first injection mode in a high-speed area of the engine.
Hysteresis is preferably provided to the switch points of the fuel injection control modes.
Specific smoothing control is preferably implemented when the fuel injection control modes are switched.
In the above-mentioned compression-ignition internal combustion engine mounted in a vehicle, damper control is implemented to prevent coupled vibration of the engine and vehicle when the fuel injection quantity changes rapidly, and when the fuel injection control modes are switched during implementation of the damper control, the fuel injection control modes are preferably switched after a specific time elapses following the start of the damper control.
The EGR performed by a EGR apparatus should preferably be carried out according to the first injection mode.
The above-mentioned compression-ignition internal combustion engine may be a common-rail diesel engine.
The present invention is a common-rail diesel engine comprising a fuel injection valve for injecting fuel into a combustion chamber in a cylinder, a common rail for constantly supplying high-pressure fuel to the fuel injection valve, and control means for controlling the injector such that the quantity and timing of the fuel actually injected through the fuel injection valve are equivalent to the target fuel injection quantity and target fuel injection timing determined in advance based on the operating conditions of the engine; wherein the control means comprises as fuel injection control modes a first injection mode in which pilot injection is carried out through the fuel injection valve with a fuel injection quantity and fuel injection timing such that the maximum rate of heat release induced by the pilot injection is 60 kJ/s or less, and main injection is then carried out through the fuel injection valve at a timing beyond the top dead center of compression; and a second injection mode in which pilot injection and main injection are carried out through the fuel injection valve on the basis of conditions that do not fulfill the conditions of the first injection mode; and the fuel injection control modes are switched such that fuel injection control is implemented in the second injection mode in the low-load areas of the engine, and fuel injection control is implemented in the first injection mode in the high-load areas of the engine.
The present invention is a method for controlling a compression-ignition internal combustion engine configured such that the quantity and timing of the fuel injected through the fuel injection valve into the combustion chamber in the cylinder is controlled based on the operating conditions of the engine; wherein the control method comprises as fuel injection control modes a first injection mode in which pilot injection is carried out through the fuel injection valve with a fuel injection quantity and fuel injection timing such that the maximum rate of heat release induced by the pilot injection is 60 kJ/s or less, and main injection is then carried out through the fuel injection valve at a timing beyond the top dead center of compression; and a second injection mode in which pilot injection and main injection are carried out through the fuel injection valve on the basis of conditions that do not fulfill the conditions of the first injection mode; and the fuel injection control modes are switched such that fuel injection control is implemented in the second injection mode in the low-load areas of the engine, and fuel injection control is implemented in the first injection mode in the high-load areas of the engine.